The field of invention relates to direct access data storage, generally. More specifically, the invention relates to the improved thermal stability of GMR based SV sensors for use within magnetic heads.
Hardware systems often include memory storage devices having media on which data can be written to and read from. A direct access storage device (DASD or disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form. Magnetic heads, when writing data, record concentric, radially spaced information tracks on the rotating disks. Magnetic heads also typically include read sensors that read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive (MR) read sensors, the defining structure of MR heads, can read stored data at higher linear densities than thin film heads. An MR head detects magnetic field(s) through the change in resistance of its MR sensor. The resistance of the MR sensor changes as a function of the direction of the magnetic flux that emanates from the rotating disk.
One type of MR sensor, referred to as a giant magnetoresistive (GMR) effect sensor, takes advantage of the GMR effect. In GMR sensors, the resistance of the MR sensor varies with direction of flux from the rotating disk and as a function of the spin dependent transmission of conducting electrons between magnetic layers separated by a non-magnetic layer (commonly referred to as a spacer) and the accompanying spin dependent scattering within the magnetic layers that takes place at the interface of the magnetic and non-magnetic layers.
GMR sensors using two layers of magnetic material separated by a layer of GMR promoting non-magnetic material are generally referred to as spin valve (SV) sensors. In an SV sensor, one of the magnetic layers, referred to as the pinned layer, has its magnetization xe2x80x9cpinnedxe2x80x9d by exchange coupling with an antiferromagnetic layer. Due to the relatively high internal ferromagnetic coupling field associated with the pinning layer, the magnetization direction of the pinning layer typically does not rotate from the flux lines that emanate from the rotating disk. The magnetization direction of the other magnetic layer (commonly referred to as a free layer), however, is free to rotate with respect to the flux lines that emanate from the rotating disk.
FIG. 1 shows a type of spin valve sensor commonly referred to as a dual spin valve sensor 100, having end regions 104 and 106 separated by a central region 102. A free layer (Free MR layer) 110 (free) is separated from two outer pinned (pinned MR layer) layers 120 (PL1) and 130 (PL2) by two SV promoting spacer layers 140 (SP1) and 150 (SP2), respectively. Referring to FIG. 1B, the magnetization 121 within the first pinned layer 120 is fixed through exchange coupling with a first antiferromagnetic (AFM1) layer 125. The magnetization 131 within the second pinned layer 130 is fixed through exchange coupling with a second antiferromagnetic (AFM) layer 135 (AFM2).
Free layer 110, spacer layers 140 and 150, pinned layers 120 and 130 and the AFM layers 125 and 135 are all formed in the central region 102. Hard bias layers 160 and 170 formed in the end regions 104 and 106, respectively, longitudinally bias the MR free layer 110. Leads 180 and 190 formed over hard bias layers 160 and 170, respectively, provide electrical connections for the flow of the sensing current Is from a current source for the MR sensor 100.
A problem with structures such as or similar to that shown in FIG. 1 is the effect of the pinned layers 120,130 on the free layer 110. Specifically, as shown in FIG. 1, magnetic fields Hd120, 130 (associated with magnetic poles at pinned layers 120, 130) as well as ferromagnetic coupling fields Hfc120, 130 (associated with xe2x80x9corange peelxe2x80x9d coupling between pinned layers 120, 130 and free layer 110) from the pinned layers 120, 130 provide a net bias on the free layer 110. Typically, the magnetic fields Hd120, 130 have more strength than the ferromagnetic coupling fields Hfc120, 130 resulting in an undesirable net field H110 at free layer 110. Net field H110 affects the orientation of magnetic moment within the free layer 110 which adversely affects the MR sensing capability of structure 100.
An apparatus, comprising a dual spin valve magnetoresistive structure having a free layer and a spacer layer between the free layer and a pinned layer. The pinned layer is between the spacer layer and the antiferromagnetic layer. There is also an offset layer, where the antiferromagnetic layer is between the offset layer and the pinned layer. The offset layer is tailored to introduce a first magnetic field that reduces a net magnetic field within said free layer.